The unstoppable advance of harlequin ladybirds

 It's now a 14 years since I first saw a harlequin ladybird in Country Durham, and a decade since I first found one in Teesdale. Yesterday, in precisely the same location, there were hundreds, feeding on ivy nectar. This abundant supply of energy in autumn, coupled with their capacity to remain active in cold weather, must surely be important factors in the phenomenal success of this invasive species. 

Harlequin larvae seem to have an affinity with sycamore, perhaps because of the vast supply of sycamore aphids that they find on the leaves. At this location sycamore and ivy grow together, which might account for the population explosion, with dense ivy also providing a sheltered winter hibernation site.

There now seem to be two dominant morphs in this local population, one black with four large, ragged red spots and the other red with multiple black spots, which is more common. 

 This species is known to be a predator of our native ladybirds and can also transmit a parasite that kills other species. It also feeds extensively on eggs of butterflies and moths. Over the last two decades it has spread rapidly, from south east England to the Scottish border. It originated in central Asia but was introduced elsewhere in misconceived biological control programmes aimed at 'environmentally friendly' aphid control in greenhouse crops. Wherever it has been introduced it has escaped and has had a detrimental effect on native insect populations.

Ivy - the all-year-round carbon dioxide fixer

Ivy's flowers provide a wonderful nectar and  pollen resource for insects in autumn (see some examples at the bottom of this post) and its berries are a vital food  resource for migrant birds in early spring, but it also has another important attribute with more general implications.

As an evergreen that stores carbon in its woody trunk, ivy is an all year-round carbon dioxide fixer, constantly removing the gas from the atmosphere. In that respect it contributes towards combatting the build-up of carbon dioxide in the atmosphere, which is the underlying cause of global climate change.

Deciduous trees like this ash have a short growing growing season in our seasonal climate. It comes into leaf in May and sheds its foliage in September, so for about half the year it fixes no carbon dioxide at all. But when it supports a luxuriant growth of ivy the two organisms together fix carbon dioxide 365 days a year.







































The combined efforts of an ash tree with ivy cladding are likely to be more effective at fixing atmospheric carbon dioxide than an ash tree alone.

The tangle of  thick, woody ivy stems on this sycamore are as effective a store of carbon as the tree's trunk.

Ivy can even turn a dead tree into a carbon dioxide fixing pillar of evergreen foliage, as it did with this dead oak at Egglestone in Teesdale a few years ago. Even better, in autumn this stump became a tower of flowers, humming with insects that came for the nectar and pollen. In spring it was covered in berries.

Another example, at Wolsingham in Weardale.

Sadly, there are still plenty of ivy-haters around who are convinced that ivy is a parasite (it isn't, it just uses trees for support). They'll usually also advance the argument that a top-heavy mass of ivy is likely to bring trees down in winter gales, but most trees that are felled in this way are moribund anyway and topple because they have already been weakened by root-rotting fungi, not by ivy. Logically, a good cladding of well-rooted ivy stems is more likely to anchor a shaky tree, delaying its demise. 

The fact that trees that have been killed by fungi often have a healthy covering of ivy suggests that it might well be resistant to some of the fungi that kill trees.

From all of this you might have gathered that I'm something of an ivy enthusiast - not least because of the insect fauna that its flowers attract in autumn. All of the pictures below were taken in a few minutes late last October on another ivy clad tree just across the road from the oak-clad stump pictured above. 

The Last Day of Winter in Teesdale

Spent the last day of winter walking beside the river Tees through woodland downstream of Egglestone Abbey in Teesdale. The pace of spring is picking up!

Sunlight streaming through hart's tongue fern fronds, revealing the herringbone pattern of sori underneath.

Ivy berries ripening fast - a fine crop, food for many birds.

Wood anemones coming into flower.

Male cones of yew releasing pollen

Golden saxifrage in full bloom.

Nectar in November

Insect numbers have plummeted since the first hard frosts arrived about a week ago, but ivy provides an almost unlimited supply of food for those few that are still active. The flowers continue to open well into December, although many of them will never be pollinated and produce berries. 

The first ivy flowers that open in September are almost all pollinated and produce berries that ripen in March, like those on the right of the picture above, whereas those that open after the first frosts, after insect numbers decline, are much less likely to be fruitful - like those on the left in the image above.

If you take a close look at ivy flowers on humid autumn mornings you can see the glistening drops of nectar on the surface of the exposed nectary ....

.... that are easily accessible to all insect visitors, including this small fly - one of the few insects that's still active. Although it can reach the nectar reward it doesn't make effective contact with the stamens and isn't well equipped with body hairs to transport pollen to that stubby stigma in the centre of the flower.

A few years ago observations on the vast range of insects that visit ivy flowers - including bees, wasps, flies and butterflies - prompted a group of researchers to investigate which of these was the most effective pollinator (see details of source publication at the end of this post). 

This is an ecologically interesting question because successful pollination in autumn leads to prolifically berry production in spring, providing an important food resource for migratory birds at a time when they need it most. The survival of some berry-eating birds in spring could hinge on the performance of insect pollinators of ivy in the previous autumn 

The researchers found that the most effective ivy pollinators were wasps. 

You can see here that a wasp is more hairy than is often supposed and it's just the right size to collect pollen as it feeds. It acts as a brush, picking up pollen and distributing it was it crawls across the flower surface, indulging in its taste for sweet nectar. 

So maybe we should rethink our attitude to those pesky, drowsy wasps that can be a painful nuisance once they abandon their nests in autumn and set out in search of anything sweet. Their late-season activity may well be playing a significant role in the lives of migratory birds..........

Source: Jacobs, J.H., Clark, S., Denholm, I., Goulson, D., Stoate, C. And Osborne, J.L. (2010).  Pollinator effectiveness and fruit set in common ivy, Hedera helix (Araliaceae). Arthropod-Plant Interactions 4 (1), 19-28.

For more on wasps, click here.

No ladybirds for months, then five species all at once.....

Thursday's Guardian Country Diary describes encounters with ladybirds in Weardale and Teesdale.

Back in the spring it seemed as though 2013 might be a good year for ladybirds locally - plenty of 7-spots seemed to have come out of hibernation so I anticipated a thriving population by the time their offspring hatched in summer - but it never seemed to materialise. I found a few isolated individuals of other species - notably 22-spot , 14-spot and an orange ladybird  but then last week .........

........ this huddle, near a pine plantation at Wolsingham in Weardale. It was the largest number of 7-spots I'd seen in one place all year: six that had chosen a split in a fence post as their hibernation site. 7-spot ladybirds aren't usually associated with conifer plantations but his particular row of fence posts, on the sheltered, south facing side of the plantation, as always been a good place to find other species. 

So it was no surprise to find this eyed ladybird - a conifer specialist - sunning itself on the same line of fence posts.

A small, unidentified fly with unusual up-turned antennae had even chosen to hitch a ride on it. The eyed ladybird is our largest species but ...

...... this one, a larch ladybird that shared the same fence post, is one of our smaller species ...

..... here going head-to-head with a staphylinid beetle (which it simply head-butted out of the way!)

Then, a day later at Egglestone in Teesdale I found ivy in full flower that had attracted several orange ladybirds, that were feeding on nectar.

You can see here the translucent pronotum of this species, that used to be considered scarce but seems to have increased in abundance in recent decades, supposedly because it has taken to feeding on fungi that grow on the honeydew secreted by sycamore aphids. On one occasion a few years ago I found a cluster of ten of this species hibernating on the bark of a sycamore in winter - it's certainly a species that can be added to the very small number of insects that are associated with sycamore, which has been present on these islands for around 500 years but has a very small insect fauna.

Close to the orange ladybirds on the ivy I then found a single 7-spot sunning itself on a fence post and ......

.......... scores of this very unwelcome addition to our ladybird fauna - the harlequin. The first time I saw these locally was in Durham city back in 2009, on ivy flowers at almost exactly this time of year. Harlequins are noted for their bewildering range of colour patterns but the indentations at the tail end of the elytra are also a distinctive feature, although they too vary in extent between individuals.

This group of about a dozen individuals had just hatched from their pupae and were still developing their full colours. Harlequins have a breeding season that extends well into autumn.

Some, that also seemed to be the most rotund individuals, were almost entirely black ...

..... but his was a more typical colour pattern in this population.

Finding another population of harlequins was an unwelcome discovery because this disease-resistant species is known to be a predator of our native ladybirds and can also transmit a parasite that kills other species. It also feeds extensively on eggs of butterflies and moths. Over the last decade it has spread rapidly from south east England to the Scottish border. It originated in central Asia but was introduced elsewhere in misconceived biological control programmes aimed at 'environmentally friendly' aphid control in greenhouse crops. Wherever it has been introduced it has escaped and has had a detrimental effect on native insect populations.

The predominantly black individuals seem to have blue eyes.

This was the last unhatched pupa, attached to the fence posts. At the point of attachment you can just see the remains of the larval skin, which is spiny in this species. 

Harlequin larvae also seem to have an affinity with sycamore, perhaps because of the vast supply of sycamore aphids that they find on the leaves - so it may well be that orange ladybirds will also form part of their diet too.

If you find harlequin ladybirds you can report their presence by contributing the record to the Harlequin Ladybird web site.

Sneaky but risky.....

This blackbird snuck in under our radar and built her nest in an ivy-covered fence within a few feet of our windows. It'll be convenient for watching her progress but tense too - a grey squirrel uses the top of the fence as a highway every day and there are magpies nesting just two gardens away...

Ivy

Rob, over at The Living Isle, on the Isle of Wight, has posted some interesting pictures of wasps visiting ivy flowers , while pictures of red admirals and honeybees on the same plants were posted by Blackbird over on Bugblog recently. Despite a frost earlier in the week, the ivy up here in the North East is still flowering well and attracting the last surviving insects - which are now mostly flies.

Ivy is so common and widespread that we tend to take it for granted but it really is one of the most important plants in the British flora. What other species provides so much nectar and pollen late in the autumn for insects, followed by berries to feed departing migrants in spring - with a dense covering of waterproof leaves through the intervening winter to provide shelter for hibernating insects?

This fly, which is showing a lot of wear-and tear on the trailing edges of its wings, is acting like a living pollination brush. The structure of the flowers, with the anthers elevated above the nectar secreting ovary, pretty much guarantees that the ivy flowers will be pollinated  ....

... as the fly stumble across the flowers, reaching down with its short proboscis, half-blinded by pollen that it's picked up. The strange musty scent of ivy, which has been likened in mouldering papers in damp cupboards, seems very attractve to flies - if you put a cut flower shoot in a room where flies are bouncing against the window, they'll soon turn their attention to the flowers and start to feed.

An Autumn Walk along the River Tees

The long, narrow gorge spanned by Egglestone's Abbey Bridge bridge provides one the most picturesque viewing points on the River Tees in autumn

This is the view from the bridge looking upstream - Egglestone Abbey is just  above the trees in the middle distance (double-click) and is ...

...... visible from the bridge now that the leaves are falling.

The view downstream - there are footpaths on both sides of the river and you can follow it down to its confluence with the River Greta, at the Meeting of the Waters.

The river squeezes through narrow gaps and tumbles over boulders ...

.... and you can hear it through the trees all the way along the path, even when it isn't in spate.

The high humidity in the gorge makes this a fine habitat for mosses and ferns like this polypody growing as an epiphyte on a tree branch over the river.

Yellowing horse chestnut leaves provide a sunbathing spot for flies whose days are numbered, now that frosts are on their way.

Nectar-rich ivy flowers provide a last-minute refuelling station for drone flies.

Shades of yellow - hazel, oak and beech autumn colours.

Some of the large beeches have been attacked by honey fungus - always fatal, but it can take decades to kill the tree.

A nuthatch, dangling down to pick beech nuts out of beech mast - it seems to be a 'mast year', with a very heavy crop.

Ripe holly berries are a reminder that there are only 50 shopping days until Christmas.

Downstream there are some wild cherries with a fiery display of autumn colours..

... and a fine crop of ripe yew berries.

A passing shower leaves a rainbow, which is wasted on those two sheep that are watching - they only have dichromatic vision and can't distinguish red from green.

Looking back upstream - on what Kenneth Grahame in the Wind in the Willows called a 'golden afternoon'...